Feature Request: skip already ignored fields

[botenvouwer]

When using structs in combination with various ORM's like GORM you'll end up having fields like: Customer and CustomerID. We ignore the Customer or the CustomerID based on what we would like to output. It would be nice to skip the fields that are explicitly set to be ignored like json:"-".

Implementing a regex would also be a fine solution: https://github.com/fatih/gomodifytags/issues/83